The present invention relates generally to suspension systems for motor vehicles and machines which receive mechanical shock and, more particularly, to a piston valving arrangement for use in shock absorbers.
Hydraulic dampers, such as shock absorbers are used in connection with motor vehicle suspension systems to absorb unwanted vibrations which occur during driving. To dampen the unwanted vibrations, shock absorbers are generally connected between the sprung portion (i.e. the vehicle body) and the unsprung portion (i.e. the suspension) of the motor vehicle. A piston assembly is located within the working chamber of the shock absorber and is connected to the body of the motor vehicle through a piston rod. The piston assembly includes a valving arrangement that is able to limit the flow of damping fluid within the working chamber when the shock absorber is compressed or extended. As such, the shock absorber is able to generate a damping force which "smooths" or "dampens" the vibrations transmitted from the suspension to the vehicle body.
The greater the degree to which the flow of damping fluid within the working chamber is restricted across the piston assembly, the greater the damping forces which are generated by the shock absorber. Accordingly, a "soft" compression and rebound stroke is produced when the flow of damping fluid across the piston assembly is relatively unrestricted. In contrast, a "firm" compression and rebound stroke is produced when there is an increased restriction to the flow of damping fluid across the piston assembly.
In selecting the damping characteristics of a shock absorber is to provide, three vehicle performance parameters are generally considered; ride comfort, vehicle handling and road holding ability. Ride comfort is largely a function of the spring constant of the main springs (i.e. coil springs, leaf springs, pneumatic spring, etc.) of the motor vehicle, as well as the spring constant of the seat, tires, and the damping of the shock absorbers. Vehicle handling is related to the variation in the vehicle's attitude (i.e. roll, pitch and yaw). For optimum vehicle handling, relatively large damping forces are required to avoid excessively rapid variation in the vehicle's attitude during high speed maneuvering, cornering, acceleration, and deceleration. Finally, road holding ability is generally a function of the amount of contact between the tires and the ground. To optimize road holding ability, large damping forces are generally required when driving on irregular surfaces to prevent loss of contact between the wheels and the ground for an excessive period of time.
As will be appreciated, a plethora of different piston valving arrangements are currently used in conventional shock absorbers. Such piston valving arrangements typically incorporate a mechanical biasing member, such as a coil spring, for biasing a flow restricting valve member so as to regulate the flow of damping fluid through a uni-directional flow path interconnecting upper and lower portions of the working chamber. While conventional piston valving arrangements generally perform satisfactorily, there is a continuing desire to reduce their complexity and cost while concomitantly maintaining the desired performance and service life characteristics. In addition, in many heavy-duty shock absorber applications, the excessively large forces generated during both the rebound and compression stroke are a design constraint in that complex hydro-mechanical valving arrangements are generally required for generating the desired damping characteristics. More particularly, many heavy-duty shock absorbers utilize a plurality of relatively thick deflectable blow-off discs or valve plates which are mechanically biased to insure adequate flow regulation in view of the large damping forces to be generated. In addition, most conventional valving arrangements incorporate independent uni-directional flow paths for regulating flow during each of the distinct rebound and compression strokes.